The present invention relates generally to video display systems and more particularly to filtering of video image data.
Some display systems utilize interlaced displays, such as televisions, to display image data generated by computers and other digital image systems. Interlaced displays display an entire display frame as a sequence of two individual fields, an odd field displaying the odd numbered rows of the display frame and an even field displaying the even numbered rows of the display frame. In this way, the fields are interlaced, and the human eye interprets the two fields shown sequentially as a complete display frame. For example, the National Television Systems Committee (NTSC) protocol for television video signals has standardized the field display rate at 60 Hz. Since there are two fields displayed per frame, the effective frame rate is 30 Hz.
The two interlaced fields may interfere when displaying small display components, such as computer text, causing flicker. Flicker is perceived when the frequency of modulated light falling on the retina of the human eye is below the Critical Fusion Frequency (CFF), which is about 72 Hz for most people. Since the field display rate, as well as the effective frame rate, of most televisions are below most people""s CFF, flicker is often noticeable and detracts from the image quality.
It is known to use a low pass filter with a cut off frequency of approximately one-fourth the display resolution to filter across the vertical direction of the entire image to minimize or eliminate flicker. However, the use of a low pass filter with such a cut off frequency may blur some items, such as text, making them unrecognizable.
Therefore, a method and or system that overcomes this problem would be useful.